Sneezes happen when irritants are able to sneak their way past our nose hairs. Our nose hairs are like our body's brooms, capturing and trapping most of the thousands of particles that we breathe in with each breath. If something irritating like dust or a cold virus gets past this broom guard, a sneeze is initiated.

A sneeze is one of the ways our bodies protect us from harm. It's a reflex that's both awkward and elegant. Awkward because of the sudden, involuntary spasms it sends us into, and elegant because of the unified efforts of our nervous and muscular systems. Working together, our nerves and muscles can forcefully blast irritants right out of our system before they can take hold and make us sick.

Pretend you're a piece of dust. You drift into someone's nose and make it past the nose hair barrier (you're a tough piece of dust!) There you tickle at nerve endings in the lining of the nose, which sends an instantaneous signal to the brain's "sneeze centre," a spot in the lower brain stem. From here quick messages go out to your eyes and to muscles of your chest and throat. Your eyes squeeze shut and the chest and throat muscles contract so powerfully that a sneeze erupts out of the mouth, clearing the nose on the way. You, piece of dust, ride out the nose at about 100 mph (160 km/h) - along with thousands of bacteria droplets.

Dust is just one of the many types of irritants that find their way into our noses every day. Pollen, animal dander, mould, and cold and flu viruses also get breathed in and sometimes expelled by sneezing. Some people "sun sneeze" when exposed to bright light. This is a genetic trait cleverly called ACHOO, which stands for autosomal dominant compelling helio-ophthalmic outburst syndrome (where did that "d" go?).

The science of sneezing is filled with fun words like "achoo" and "sternutation." The latter word is a scientific word for sneezing, coming from the Latin term "sternuo." "Snatiation" is a rarer thing: sneezing triggered by a full stomach right after eating, another genetic trait. The origin of that one? It comes from a blend of "sneezing" and "satiation" (which means fullness) - the researcher who invented the term suggested it be remembered with "Sneezing Noncontrollably At a Time of Indulgence of the Appetite - a Trait Inherited and Ordained to be Named." Hmm.

People also commonly use the German word "gesundheit" when someone sneezes, giving a blessing of good health. (Other cultures use similar wishes of good health - for instance, "na zdrowie" in Polish and "sláinte" in Gaelic.) Others just say "Bless you!"

A sneeze itself is a mixed blessing. Though a sneeze protects the sneezer, it can make other people sick. When you sneeze, you blast all those bacterial droplets into the air and onto the skin and tissue of anyone in the vicinity of the sneeze. Which brings us to our list of sneeze etiquette and self-care:

Cover your mouth to catch a sneeze before it gets to someone else. Sneezing into a tissue is best, since you can toss the germy rag into the trash when you're done. If you don't have tissue, try not to use your hand to shield the sneeze. Rather, aim for the inside of your elbow or into the crook of your shoulder. You're less likely to touch doorknobs and ATM machines with those parts of your body, right?

If you sneeze in your hand, make sure to wash with soap and water for at least 15 to 20 seconds or use a hand sanitizer before touching other things.

It's hard to avoid all sneeze triggers, especially during the contagious cold and flu season. Covering up with scarves or face-masks is how some people defend their noses.

You can also steer your nose clear of certain environmental sneeze makers. If pet dander is causing sneezing, keep pets outdoors. Check around your home to make sure filters are clear and that there is no mould. Try not to go out much on high pollen count days.

A polite "excuse me" doesn't hurt after you've had a loud sneeze fit in a public place. When it comes to "blessing" someone after a sneeze, keep in mind that different parts of the world recognize different customs.